1. Field of the Invention
The present invention relates generally to a method and apparatus for performing a coronary artery bypass procedure. More particularly, the present invention performs a coronary artery bypass utilizing a number of approaches including an open-chest approach (with and without cardiopulmonary bypass), a closed-chest approach under direct viewing and/or indirect thoracoscopic viewing (with and without cardiopulmonary bypass), and an internal approach through catheterization of the heart and a coronary arterial vasculature without direct or indirect viewing (with and without cardiopulmonary bypass).
2. Description of the Prior Art
Coronary artery disease is the leading cause of premature death in industrialized societies. But the mortality statistics tell only a portion of the story; many who survive face prolonged suffering and disability.
Arteriosclerosis is "a group of diseases characterized by thickening and loss of elasticity of arterial walls." DORLAND'S ILLUSTRATED MEDICAL DICTIONARY 137 (27th ed. 1988). Arteriosclerosis "comprises three distinct forms: atherosclerosis, Monckeberg's arteriosclerosis, and arteriolosclerosis." Id.
Coronary artery disease has been treated by a number of means. Early in this century, the treatment for arteriosclerotic heart disease was largely limited to medical measures of symptomatic control. Evolving methods of diagnosis, coupled with improving techniques of post-operative support, now allow the precise localization of the blocked site or sites and either their surgical re-opening or bypass.
The re-opening of the stenosed or occluded site can be accomplished by several techniques. Angioplasty, the expansion of areas of narrowing of a blood vessel, is most often accomplished by the intravascular introduction of a balloon-equipped catheter. Inflation of the balloon causes mechanical compression of the arteriosclerotic plaque against the vessel wall. Alternative intravascular procedures to relieve vessel occlusion include atherectomy, which results in the physical desolution of plaque by a catheter equipped (e.g. a cutting blade or high-speed rotating tip). Any of these techniques may or may not be followed by the placement of mechanical support and called a "stent," which physically holds the artery open.
Angioplasty, and the other above-described techniques (although less invasive than coronary artery bypass grafting) are fraught with a correspondingly greater failure rate due to plaque reformation. Contemporary reports suggest re-stenosis is realized in as many as 25 to 55 percent of cases within 6 months of successful angioplasty. See Bojan Cercek et al., 68 AM. J. CARDIOL. 24C-33C (Nov. 4, 1991). It is presently believed stenting can reduce the re-stenosis rate.
A variety of approaches to delay or prevent re-blockage have accordingly evolved. One is to stent the site at the time of balloon angioplasty. Another is pyroplasty, where the balloon itself is heated during inflation. As these alternative techniques are relatively recent innovations, it is too early to tell just how successful they will be in the long term. However, because re-blockage necessitates the performance of another procedure, there has been renewed interest in the clearly longer-lasting bypass operations.
The current indications for coronary artery bypass grafting have been outlined. See LUDWIG K. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 4-5 (1990). Criteria vary dependent upon whether the intent is therapeutic (that is, to reverse cardiac compromise in the patient currently suffering symptoms), or prophylactic (that is, to prevent a potentially fatal cardiac event from occurring in someone who is, at present, symptom free). Id.
The traditional open-chest procedure requires an incision of the skin anteriorly from nearly the neck to the navel, the sawing of the sternum in half longitudinally, and the spreading of the ribcage with a mechanical device to afford prolonged exposure of the heart cavity. If both lungs are deflated, a heart-lung, or cardiopulmonary bypass procedure, is also necessary.
Depending upon the degree and number of coronary vessel occlusions, a single, double, triple, or even greater number of bypass procedures may be necessary. Often each bypass is accomplished by the surgical formation of a seperate conduit from the aorta to the stenosed or obstructed coronary artery, at a location distal to the diseased site. A major obstacle has been the limited number of vessels that are available to serve as conduits. Potential conduits include the two saphenous veins of the lower extremities, the two internal thoracic arteries under the sternum, and the single gastroepiploic artery in the upper abdomen. Theoretically, if all of these vessels were utilized, the procedure would be limited to a quintuple (5-vessel) bypass. Because of this, newer procedures using a single vessel to bypass multiple sites have evolved. However, this technique is fraught with its own inherent hazards, though. When a single vessel is used to perform multiple bypasses, physical stress (e.g., torsion) on the conduit vessel can result. Such torsion is particularly detrimental when this vessel is an artery.
Unfortunately, attempts at using vessels from other species (xenografts), or other non-related humans (homografts) has been largely unsuccessful. See LUDWIG K. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 38-39 (1990). Similarly, trials with synthetic alternatives have not been encouraging. See Id. at 39.
While experimental procedures transplanting alternative vessels continue to be performed, in general clinical practice there are five vessels available to use in this procedure over the life of a particular patient. Once these "spare" vessels have been sacrificed, there is little or nothing that modern medicine can offer. It is unquestionable that new methods, not limited by the availability of such conduit vessels, are needed.
In the past, the normal contractions of the heart have usually been stopped during suturing of the bypass vasculature. This can be accomplished by either electrical stimulation which induces ventricular fibrillation, or through the use of certain solutions, called cardioplegia, which chemically alter the electrolytic milleau surrounding cardiac muscles. Stoppage of the heart enhances visualization of the coronary vessels, while removing the need for blood flow through the coronary arteries during the procedure. This provides the surgeon with a "dry field" in which to operate and create a functional anastomosis. After the coronary artery bypass procedure is completed, cardioplegia is reversed, and the heart electrically stimulated if necessary. As the heart resumes the systemic pumping of blood, the cardiopulmonary bypass is gradually withdrawn. The seperated sternal sections are then re-joined, and the overlying skin and saphenous donor site or sites (if opened) are sutured closed.
The above-described procedure is highly traumatic. Immediate post-operative complications include infection, bleeding, renal failure, pulmonary edema and cardiac failure. The patient must remain intubated and under intensive postoperative care. Narcotic analgesia is necessary to alleviate the pain and discomfort.
The most troubling complication, once the immediate post-surgical period has passed, is bypass vessel re-occlusion. This has been a particular problem with bypass grafting of the left anterior descending coronary artery when the saphenous vein is employed. Grafting with the internal thoracic (internal mammary) artery results in long-term patency rate superior to saphenous vein grafts, particularly when the left anterior descending coronary artery is bypassed. Despite this finding, some cardiothoracic surgeons continue to utilize the saphenous vein because the internal thoracic artery is smaller in diameter and more fragile to manipulation; thus making the bypass more complex, time-consuming, and technically difficult. Additionally, there are physiological characteristics of an artery (such as a tendency to constrict) which increases the risk of irreversible damage to the heart during the immediate period of post-surgical recovery.
Once the patient leaves the hospital, it may take an additional five to ten weeks to recover completely. There is a prolonged period during which trauma to the sternum (such as that caused by an automobile accident) can be especially dangerous. The risk becomes even greater when the internal thoracic artery or arteries, which are principle suppliers of blood to the sternum, have been ligated and employed as bypass vessels.
Due to the invasive nature of the above technique, methods have been devised which employ contemporary thoracoscopic devices and specially-designed surgical tools to allow coronary artery bypass grafting by closed-chest techniques. While less invasive, all but the most recent closed-chest techniques still require cardiopulmonary bypass, and rely on direct viewing by the surgeon during vascular anastomoses. These methods require a very high level of surgical skill together with extensive training. In such situations, the suturing of the bypassing vessel to the coronary artery is performed through a space created in the low anterior chest wall by excising the cartilaginous portion of the left fourth rib. Also, as they continue to rely on the use of the patient's vessels as bypass conduits, the procedures remain limited as to the number of bypasses which can be performed. Because of these issues, these methods are not yet widely available.
In view of the above, it would be desirable to provide other methods or techniques by which adequate blood flow to the heart could be re-established which do not rely on the transposition of a patient's own arteries or veins. It would also be desirable to provide other methods or techniques by which adequate blood flow to the heart could be re-established which results in minimal tissue injury. It would be particularly desirable if such methods or techniques did not require opening of the chest by surgical incision of the overlying skin and the division of the sternum. It would be even more desirable if such methods or techniques did not require surgical removal of cartilage associated with the left fourth rib, did not require the surgical transection of one or both internal thoracic arteries, did not require the surgical incision of the skin overlying one or both lower extremities, and did not require the surgical transection and removal of one or both saphenous veins. It would also be desirable if such methods or techniques could be performed without stoppage of the heart, and without cardiopulmonary bypass.
The conventional surgical procedures (such as those described above) for coronary artery bypass grafting using saphenous vein or internal thoracic artery via an open-chest approach have been described and illustrated in detail. See generally Stuart W. Jamieson, Aortocoronary Saphenous Vein Bypass Grafting, in ROB & SMITH'S OPERATIVE SURGERY: CARDIAC SURGERY, 454-470 (Stuart W. Jamieson & Norman E. Shumway eds., 4th ed. 1986); LUDWIG K. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 48-80 (1990). Conventional cardiopulmonary bypass techniques are outlined in Mark W. Connolly & Robert A. Guyton, Cardiopulmonary Bypass Techniques, in HURST'S THE HEART 2443-450 (Robert C. Schlant & R. Wayne Alexander eds., 8th ed. 1994). Coronary artery bypass grafting, utilizing open-chest techniques but without cardiopulmonary bypass, is described in Enio Buffolo et al., Coronary Artery Bypass Grafting Without Cardiopulmonary Bypass, 61 ANN. THORAC. SURG. 63-66 (1996)
Some less conventional techniques (such as those described above) are performed by only a limited number of appropriately skilled practitioners. Recently developed techniques by which to perform a coronary artery bypass graft utilizing thoracoscopy and minimally-invasive surgery, but with cardiopulmonary bypass, are described and illustrated in Sterman et al., U.S. Pat. No. 5,452,733 (1995). An even more recent coronary artery bypass procedure employing thoracoscopy and minimally-invasive surgery, but without cardiopulmonary bypass, is described and illustrated by Tea E. Acuff et al., Minimally Invasive Coronary Artery Bypass Grafting, 61 ANN. THORAC. SURG. 135-37 (1996).
Methods of catheterization of the coronary vasculature, techniques utilized in the performance of angioplasty and atherectomy, and the variety of stents in current clinical have been described and illustrated. See generally Bruce F. Waller & Cass A. Pinkerton, The Pathology of Interventional Coronary Artery Techniques and Devices, in 1 TOPOL'S TEXTBOOK OF INTERVENTIONAL CARDIOLOGY 449-476 (Eric J. Topol ed., 2nd ed. 1994); see also David W. M. Muller & Eric J. Topol, Overview of Coronary Athrectomy, in 1 TOPOL'S TEXTBOOK OF INTERVENTIONAL CARDIOLOGY at 678-684; see also Ulrich Sigwart, An Overview of Intravascular Stents: Old & New, in 2 TOPOL'S TEXTBOOK OF INTERVENTIONAL CARDIOLOGY at 803-815.
Finally, some techniques remain in the experimental stages, and are limited to animal testing. Direct laser canalization of cardiac musculature (as opposed to canalization of coronary artery feeding the cardiac musculature) is described in Peter Whittaker et al., Transmural Channels Can Protect Ischemic Tissue: Assessment of Long-term Myocardial Response to Laser- and Needle-Made Channels, 94(1) CIRCULATION 143-152 (Jan. 1, 1996).